Coma(1978) [Mrs. Nancy 'Nance' Greenly]: Poisoned by being given carbon monoxide instead of oxygen during surgery, so that her organs can be harvested. (Thanks to Scheck)

Death on the Nile (1978) [Linnet Ridgeway Doyle]: Shot in the head by Simon MacCorkindale while asleep in bed. Her body is discovered afterwards by Jane Birkin, then examined by Jack Warden and Peter Ustinov. The murder is depicted in several hypothetical flashbacks showing how it could have happened, before the final flashback showing how it actually happened.Creepshow 2(1987) [Annie Lansing]: Killed by the zombie Tom Wright when she gets home after killing him in a hit-and-run accident. (It's been so long since I've seen this movie, I can't recall any details.) (Thanks to Robert)

Curdled (1996) [Katrina Brandt]: Stabbed in the back by William Baldwin while she's crawling on the floor (already gravely wounded).